Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$182.67	7.610%	$196.5712	$196.57	$196.55	$196.60
Purchase #2	$127.90	6.758%	$136.5435	$136.54	$136.55	$136.50
Purchase #3	$101.86	8.644%	$110.6648	$110.66	$110.65	$110.70
Purchase #4	$76.65	7.579%	$82.4593	$82.46	$82.45	$82.50
Purchase #5	$158.94	9.217%	$173.5895	$173.59	$173.60	$173.60
Purchase #6	$85.40	6.674%	$91.0996	$91.10	$91.10	$91.10
Purchase #7	$42.82	9.861%	$47.0425	$47.04	$47.05	$47.00
7 purchase totals =	$776.24		$837.9704	$837.96	$837.95	$838.00